Whenever light travels from one medium to another, some portion of the light is reflected from the interface between the two media. For example, about 4-5% of the light shining on a clear plastic substrate is reflected at the top surface.
Different approaches have been employed to reduce the reflection of polymeric materials. One approach is to use antireflective (AR) coatings such as multilayer reflective coatings consisting of transparent thin film structures with alternating layers of contrasting refractive index to reduce reflection. It has proven difficult to achieve broadband antireflection using AR coatings, however.
Another approach involves using subwavelength surface structure (for example, subwavelength scale surface gratings) for broadband antireflection. The methods for creating the subwavelength surface structure tend to be complicated and expensive batch processes, however. For example, the method disclosed in U.S. Patent Application Publication No. 2005/0233083 involves bombarding a polymeric surface with Ar/O2 plasma under vacuum conditions of less than 0.5 mTorr. This requirement of extreme vacuum conditions limits the commercial viability of the method.